Basically, a digital bit rate converter converts the bit rate of an applied digital signal by either increasing or decreasing the time period allocated to each bit. Such converters are commonly used in digital transmission systems as interface devices. A digital repeatered transmission facility normally has only a narrow band of frequencies over which it operates satisfactorily, and frequently the bit rates of data sources are outside the operable frequency range of such transmission facilities. When a data source cannot be modified to operate at the facility rate, a bit rate converter of the type discussed herein must be used, to interface the data source with the transmission line.
Unfortunately, the prior-art converter systems are relatively complex arrangements. Furthermore, they do not always make full use of the communication channel provided. In an arrangement disclosed in U.S. Pat. No. 3,548,309, issued to B. R. Saltzberg, et al, on Dec. 15, 1970, the message bit stream is simply sampled at the line rate, and the redundant samples are transmitted along with the nonredundant samples. A complex receiver then blocks the redundant samples to recover the original signal. Such a system is wasteful of the information-carrying capacity of the transmission channel since redundant samples are transmitted with the information signal.
One objective of this invention is to provide a system for increasing the bit rate of a digital bit stream to a higher bit rate to permit transmission over a digital communication facility.
It is another object of this invention to provide a digital receiver capable of separating the original data bit stream from the transmitted composite line signal.